Centrifuge test tube stopper

ABSTRACT

AN EASILY ASSEMBLED AND DISASSEMBLED CENTRIFUGE SAMPLE HOLDER INCLUDING A SAMPLE CONTAINER AND A STOPPER ASSEMBLY WHICH FITS SNUGLY INSIDE THE MOUTH OF THE CONTAINER AND CARRIES AN O-RING FOR FORMING A LIQUID-TIGHT SEAL ABOUT THE INNER SURFACE OF THE CONTAINER WITH THE STOPPER ASSEMBLY HAVING ITS OUTER DIMENSIONS NO GREATER THAN THE DIMENSION OF THE CYLINDRICAL INNER SURFACE INSIDE THE MOUTH OF THE CONTAINER SO THAT SAID STOPPER ASSEMBLY IS MOVABLE TO A MULTITUDE OF POSITIONS ALONG THE INNER CYLINDRICAL SURFACE UNTIL THE LOWER SURFACE OF THE STOPPER ABUTS AGAINST THE SURFACE OF THE SAMPLE SOLUTION WHICH THEREBY SUPPORTS THE STOPPER ASSEMBLY IN THE DIRECTION OF THE AXIS OF THE SAMPLE CONTAINER AGAINST THE FORCES OF CENTRIFUGATION DURING OPERATION OF THE CENTRIFUGE.

arch 13, 1973 LVGRQPPER ETAL 3,720,502

- CENTRIFUGE TEST TUBE STOPPER Filed Dec. 21, 1970 Fi 2 INVENTORS. g 'LEE GROPPER BY LAWRENCE E. STAHL EMA/# United States Patent Inc.

Filed Dec. 21, 1970, Ser. No. 100,005 Int. Cl. B011 3/00 U.S. Cl. 23-292 3 Claims ABSTRACT OF THE DISCLOSURE A11 easily assembled and disassembled centrifuge sample holder including a sample container and a stopper assembly which fits snugly inside the mouth of the container and carries an O-ring for forming a liquid-tight seal about the inner surface of the container with the stopper assembly having its outer dimensions no greater than the dimension of the cylindrical inner surface inside the mouth of the container so that said stopper assembly is movable to a multitude of positions along the inner cylindrical surface until the lower surface of the stopper abuts against the surface of the sample solution which thereby supports the stopper assembly in the direction of the axis of the sample container against the forces of centrifugation during operation of the centrifuge.

BACKGROUND OF THE INVENTION Field of the invention This invention relates in general to centrifuges of the type in which the material to be subjected to centrifugation is held within sample containers, such as test tubes or bottles, carried by the centrifuge rotor and more particularly to an improved centrifuge sample container and stopper assembly.

Description of the prior art Preparative centrifuges commonly employ a rotor having a series of cavities equally spaced about the circumference of the rotor body and adapted to receive containers (test tubes or bottles) for carrying the sample to be centrifuged. Typically in a preparative centrifuge rotor the axis of each cavity is inclined at an angle with respect to the vertical rotational axis of the rotor such that the bottom of the container is disposed further away from the rotor axis than the top of the container. Such rotors are commonly referred to as fixed angle rotors and are advantageous in that initially precipitate is collected at the bottom of the container at a more rapid rate than if a container having its longitudinal axis orientated perpendicular to the rotor axis were utilized.

During rotor operation the sample climbs up the centrifugal (outermost) side of the container wall. Eventually when a sufficiently high rotational speed is reached, the surface of the sample stands almost parallel with the rotor axis. As such it is evident that, if the container used in the fixed angle rotor is initially full or almost so, leakage from the sample at the top of the container will occur unless there is provided a suitable cap for forming a liquid-tight seal.

An ideal cap for a centrifuge test tube (or bottle) container exhibits characteristics of high strength, leak-tightness, and simplicity of assembly and disassembly. High strength is necessary to withstand the high centrifugal forces to which the container and cap assembly or stopper is subjected when the rotor is spun at the high rotational speeds, typically 40,000 r.p.m. and upward, reached during the course of routine centrifuge operation. Moreover, the container and cap assembly or stopper must remain leak-tight during the centrifuge operation notwithstanding the high centrifugal forces generated, in order to prevent cross-contamination and to protect operating personnel from any virulent components of the sample material.

Further, in many scientific biological investigations it is necessary to centrifuge literally thousands of individual samples. This is where simplicity and ease of assembly and disassembly of the container and cap combination come into play. The simpler and easier the assembly and disassembly, the quicker the container may be loaded and unloaded resulting in a large saving of time and cost to the operator.

Typically, prior art centrifuge test tube and bottle caps have been fabricated from relative high strength materials, such as steel, and least partially supported by a shoulder or ridge formed in the upper portion of the centrifuge rotor cavity in which the container is placed. Such measures were considered necessary to enable the container and cap assembly or stopper to resist distortion under the high centrifugal forces to which it is subjected during centrifugation. Examples of conventional prior art centrifuge sample containers and cap assemblies may be found in US. Pat. Nos. 3,459,369; 3,447,712; 3,366,- 320; 3,071,316; and 2,649,245. Prior art designs are characterized by two serious drawbacks. First, the cap generally must be screwed onto a threaded surface formed on the container which consumes valuable time. Secondly, an appropriate ridge or shoulder formed in the rotor cavity to assist in cap support inherently limits that rotor to the use of test tubes (or bottles) of one length since the closed end of the sample container must conform to and be in contact with the lower extremities of the cavity to prevent distortion of the container.

SUMMARY The present invention contemplates a centrifuge container and stopper assembly which is simple in construction, able to maintain a liquid-tight seal under the high centrifugal forces generated during centrifugation, and easily and quickly assembled and disassembled. To this end, in accordance with the principles of the present invention, the centrifuge container and stopper assembly includes an appropriate shaped container with a stopper or plug element which fits snugly inside the mouth of the container. The stopper element carries an O-ring which forms a liquid-tight seal about the inner surface of the container. Once the container is filled with the sample solution (under investigation) the stopper assembly is inserted to a depth such that the lower surface of the stopper abuts against the surface of the sample solution, or the sample solution is filled to a depth such that the surface of the sample solution abuts against the lower surface of the stopper, and the solution thereby supports the stopper against the forces of centrifugation during the centrifuge run. The stopper element also includes a cylindrical axial bore, through which sample solution may be introduced into the test tube until it abuts against the lower surface of the stopper assembly, and a counterbore concentric with the axial bore into which a plug member slidably fits to close the axial bore once the tube is filled.

Accordingly, a primary object of the present invention is the provision of an improved centrifuge container and stopper assembly which is simple in construction, limited in number of components, and easily and quickly assembled and disassembled.

A further object is the provision of a centrifuge container and stopper assembly wherein the stopper is supported in the direction of the axis of the centrifuge container by the sample solution held within the container during a centrifuge run and does not require ancillary support means in the rotor body itself.

Still a further object is the provision of a centrifuge container and stopper assembly which permits sample containers of varying lengths to be used with the same fixed angle preparative rotor.

These and other objects and advantages of the invention will become apparent from the following detailed description read in conjunciton with the accompanying drawings in which:

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view of a fixed angle type preparative centrifuge rotor loaded with test tube and stopper assemblies constructed in accordance with the principles of the present invention.

FIG. 2 is an axial sectioanl view of the centrifuge test tube and stopper assembly with the stopper in place over the mouth of the tube.

FIG. 3 is an exploded view of the stopper assembly.

At the outset it should be emphasized that while the contrifuge sample container is illustrated and described as a test tube in the ensuing discussion, this is solely for descriptive purposes and other sample containers, such as bottles or the like, may be utilized in the present invention.

With reference now to the drawings and more specifically to FIG. 1 it will be observed that the reference numeral designates a typical preparative centrifuge rotor having a plurality of U-shaped cavities or wells 11 having a U-shaped cross-section equally spaced about the circumference of the rotor 10 and adapted to receive and carry centrifuge test tube and cap assemblies containing the solution to be centrifuged. Each cavity 11 (and accordingly each test tube and cap assembly 15) projects downwardly from and at some predetermined angle with respect to rotational axis 12 of rotor 10. As will become apparent, in accordance with the principles of the present invention, a ridge or shoulder means or other auxiliary support for the test tube cap assembly is not required thereby enabling the rotor 10 to accommodate test tubes of varying lengths.

As may be best seen in FIGS. 2 and 3 the centrifuge test tube having a U-shaped cross-section and cap assembly 15 comprises a U-shaped test tube 16 and a cap assembly 17. The base or lower end of test tube 16 is contoured to conform with the bottom of cavity 11 in which the test tube 16 is placed. This assists in preventing distortion of the lower extremities of the tube during centrifugation.

Stopper assembly 17 includes a generally cylindrical stopper member or plug 18 which fits snugly inside the mouth of test tube 16 and is slidably inserted and removed therefrom. Stopper member 18 includes an annular groove 19 about its outer surface for carrying and an 'O-ring seal 20. O-ring 20 is slightly larger in diameter than annular groove 19 such that once stopper member 18 is inserted into the mouth of test tube 16, O-ring 20 presses against the inner surface of test tube 16 to form a liquid-tight seal. Both test tube 16 and stopper member 18 are fabricated from a suitable plastic, such as polycarbonate, to permit the test tube and cap assembly to carry a sample solution which might react with metallic ions.

Stopper member 18 also includes a generally circular axial bore 21 which communicates with the interior of test tube 16 to permit the introduction of the sample solution into the test tube after the stopper member 18 has been inserted into the mouth of tube 16. A circular counterbore 22 slightly greater in diameter than axial bore 21 is provided concentric with axial bore 21 to form a flat annular shoulder or seat 23 (orthogonal with respect to the vertical axis of tube 16) which serves as a seat for a plug member 24. Plug member 24, which slidably fits into counterbore 22, includes a generally cylindrical body portion 30 dimensioned to fit snugly inside counterbore 22 with a Hat lower surface 311 which seats against shoulder 23. A circular stem 32 projects downwardly from the center of lower surface 31 and serves to close axial bore 21 once the plug member 24 is inserted into counterbore 22. To form a liquidtight seal a small O-ring 33- is sandwiched between lower surface 31 and seat 23. Like test tube 16 and stopper member 18, plug 24 is fabricated of plastic.

A depending skirt 25 projects downwardly from the main body portion 28 of the stopper member 18. The under surface 26 of the main body portion 28 slopes downwardly and outwardly at some predetermined angle between axial bore 21 and skirt 25. This inclined under surface 26 facilitates the release of air bubbles while the test tube is being filled with sample solution. Finally, stopper member 18 also includes an externally threaded axial stud 27 projecting upwardly from the upper surface 29 of stopper member 18 so that an appropriate tool may be threadedly engaged with stopper member 18 to facilitate its removal after the centrifuge run.

It will be appreciated that the present invention provides a relatively simple centrifuge test tube and cap assembly which may be easily and quickly assembled and disassembled. The test tube 16 is capped by merely placing the test tube in a suitable holder and inserting cylindrical stopper member 18 into the mouth of the tube by hand or with a suitable loading tool. The tube is then filled with sample solution through aixal bore 21 and plug 24 slidably inserted into counterbore 22 to close bore 21 and complete the capping of the tube. After centrifugation an appropriate removing tool is screwed onto stud 27 to extract the tube from the rotor cavity and to remove the stopper member 18 from the mouth of the tube. This simple assembly and disassembly enables the operator to load and unload centrifuge test tube 16 much quicker than heretofore possible resulting in considerable savings in time and cost.

It is significant to note that once the stopper member 18 is in place and the test tube '16 has been filled with the sample solution to be investigated, the under surface 26 of stopper member 18 is in contact with the sample solution and supported in the direction of the axis of the tube by such solution during centrifugation. That is, there is no ancillary axial support for the cap assembly 17. It is preferable that the effective weight of stopper assembly 17 during a centrifugation run be slightly greater than the pressure developed by the sample solution contained within the test tube 16 such that the stopper assembly 17 compresses the solution slightly. However, this is not essential but, if the effective weight of the stopper assembly 17 is less than the pressures developed by the solution under investigation, the stopper assembly 17 will tend to float, in which case the rotor lid or some other means must be utilized to retain the stopper in the tube.

Numerous modifications and departures from the specific apparatus described herein may be made by those skilled in the art without departing from the inventive concept of the invention. For instance, as previously emphasized the cap assembly of the present invention may be utilized with sample containers other than test tubes, such as bottles. Accordingly, the invention is to be construed as limited only by the spirit and scope of the appended claims.

What is claimed is:

1. A centrifuge sample container and stopper assembly adapted to be carried by a centrifuge rotor, the combination comprising: a sample container for containing a sample solution to be investigated by centrifugation, said container having a mouth and a substantially cylindrical inner surface adjacent the mouth of said container, a stopper member having upper and lower surfaces and having an outer cylindrical surface positioned snugly within the cylindrical surface of said container, said stopper member having an annular groove around its outer surface and an axial bore therein through which sample solution may be introduced into said sample container, an O-ring seal carried by said annular groove to form a liquid-tight seal between said cylindrical inner surface of said sample container and said outer cylindrical surface of said stopper member, a generally circular counterbore in said stopper member concentric with the axis of said axial bore, said counterbore being greater in diameter than said axial bore to form an annular shoulder substantially orthogonal to the axis of said axial bore, said stopper assembly including a generally cylindrical plug member inserted into said counterbore of said stopper member, said plug member having a lower surface seated against said annular shoulder and a circular stern protruding from said lower surface and extending into said axial bore, said stem forming a liquid tight seal closing said axial bore, said stopper assembly having an outer dimension when inserted no greater than the diameter of said cylindrical inner surface so that said stopper assembly is movable to a multitude of positions along said cylindrical surface of said container until said lower surface of said stopper abuts against the surface of the sample solution in said container and the sample solution thereby supports said cap assembly in the direction of the axis of said sample container against the forces of centrifugation during operation of the centrifuge.

2. A centrifuge sample container and stopper assembly as claimed in claim 1 whereinsaid sample container comprises a test tube U-shaped in cross-section.

3. A centrifuge sample container and stopper assembly as defined in claim 1 wherein said plug member further includes an externally threaded stud projecting upwardly from said upper surface.

References Cited UNITED STATES PATENTS 3,459,369 8/1969 Marks 233-26 3,434,615 3/1969 Barcetta 215-47 1,643,285 9/1927 Davis 215--74 793,321 6/1905 Renner 21573 JAMES R. BOLE-R, Primary Examiner G. H. KRIZMANICH, Assistant Examiner U.S. Cl. X.R. 23326 

